The following code (thanks to @Rohi Namjoshi) does what I intend to do but with few caveats:

Row[{
  jdata[GroupBy[Key["country"]], All, {"Exposure index", "EVI"}] // 
       Map[Quantity[100.*(Last@# - First@#)/First@#, "Percent"] &], Spacer[10],
  jdata[GroupBy[Key["country"]], Mean, {"Exposure index", "EVI"}]
    }]

as you can see from the output table, I am not able to cleanly present the calculations in columns. Indicator names should be column names and the associated calculations should be elements of columns. The first table corresponds to percentage changes and the latter one to mean for each country.

Also, I could not solve the Missing[Key]` problem due to missing data for either the initial year or last year.

The following code (thanks to @Rohi Namjoshi) does what I intend to do but with few caveats:

Row[{
  jdata[GroupBy[Key["country"]], All, {"Exposure index", "EVI"}] // 
       Map[Quantity[100.*(Last@# - First@#)/First@#, "Percent"] &], Spacer[10],
  jdata[GroupBy[Key["country"]], Mean, {"Exposure index", "EVI"}]
    }]

as you can see from the output table, I am not able to cleanly present the calculations in columns. Indicator names should be column names and the associated calculations should be elements of columns. The first table corresponds to percentage changes and the latter one to mean for each country.

Also, I could not solve the Missing[Key] problem due to missing data for either the initial year or last year.

The following code (thanks to @Rohi Namjoshi) does what I intend to do but with few caveats:

Row[{
  jdata[GroupBy[Key["country"]], All, {"Exposure index", "EVI"}] // 
       Map[Quantity[100.*(Last@# - First@#)/First@#, "Percent"] &], Spacer[10],
  jdata[GroupBy[Key["country"]], Mean, {"Exposure index", "EVI"}]
    }]

as you can see from the output table, I am not able to cleanly present the calculations in columns. Indicator names should be column names and the associated calculations should be elements of columns. The first table corresponds to percentage changes and the latter one to mean for each country.

The following code (thanks to @Rohi Namjoshi) does what I intend to do but with few caveats:

Row[{
  jdata[GroupBy[Key["country"]], All, {"Exposure index", "EVI"}] // 
       Map[Quantity[100.*(Last@# - First@#)/First@#, "Percent"] &], Spacer[10],
  jdata[GroupBy[Key["country"]], Mean, {"Exposure index", "EVI"}]
    }]

as you can see from the output table, I am not able to cleanly present the calculations in columns. Indicator names should be column names and the associated calculations should be elements of columns. The first table corresponds to percentage changes and the latter one to mean for each country.

Also, I could not solve the Missing[Key]` problem due to missing data for either the initial year or last year.